1. Field of the Invention
The invention is directed to a method to deconvolve the influence of variable height (topography) from the variation of a sample property such as sheet resistance, dielectric constant, magnetic permeability, etc., in scans taken with scanning devices such as a near-field scanning microwave microscope. Such scanning devices like a microwave microscope simultaneously measures two quantities during a scan. These two quantities can include frequency shift error signal from a feedback loop (xcex94f), and the quality factor of the microscope resonator (Q). The invention utilizes this data to uniquely determine a physical property of the sample, as well as its topography. This Application claim benefit to provisional Application No. 60/124,300 Mar. 12, 1999.
2. Background of the Invention
In trying to measure a sample property, such as sheet resistance, with precision scanning devices, variations in the sample property will show up in both the feedback loop (xcex94f) and quality factor (Q) data. However, in addition, variations in sample topography, which cause the height h (the separation between the probe and the sample) to be variable, will also influence the xcex94f and Q data. Therefore, conventional systems and methods may mistakenly interpret variations in data as coming from sample property variations, when in fact it is coming from topography. The present invention, therefore, addresses the need to uniquely separate the influences of sample topography and sample property variations into two separate images.
In order to provide the advantages noted above, a method of disentangling sample properties in a scanned sample comprises scanning a calibration sample on a sample stage, with the calibration sample being scanned in a direction of variation of a sample property of interest. The scan is performed at a plurality of heights. Values representing a first variable and a second variable are recorded for the calibration sample during the scan. Quantitative measurements of the sample property of interest are made using an independent means at a plurality of points across the calibration sample. The quantitative measurements are used to generate calibration data regarding the first variable and the second variable for the calibration sample, such that effects due to sample topography are eliminated from the recorded data. Conversion functions are mathematically determined using the calibration data, to convert the first and second measured variables into height and the sample property of interest. An unknown sample is scanned, and the first variable and second variable are measured during the scan, and recorded. An image of the sample property of interest for the unknown sample is mathematically determined by combining the conversion functions with the first variable and second variable for the unknown sample.
The method also includes the steps noted above, wherein the first variable is frequency shift and the second variable is quality factor Q, and wherein the property of interest is sheet resistance.
In a second embodiment of the invention, the sample is held in contact with the probe, so that height is no longer a variable. In this embodiment, there are two sample properties, and topography no longer has an effect.
This invention can be utilized, for example, with a probe which is a coaxial cable with an open end, or with a probe which is a coaxial cable with the center conductor connected to the outer conductor by a loop.